GB2234636A - Radio frequency shielding - Google Patents

Abstract

A room is shielded from radiation of radio frequency by screening individual components of an existing room. A false ceiling (15), walls (12, 13), and floor (9) are laid over the existing ones and incorporate lightweight shielding in the form of copper mesh (14, 18, 24). Secondary glazing (19) is applied over existing windows (6), and a screened door (7) is used. This enables an existing room to be shielded whilst retaining windows and doors. Glazing units and doors for screening or shielding are also disclosed. <IMAGE>

Description

RADIO FREQUENCY SHIELDING This invention relates to shielding for electromagnetic waves of radio frequency, in particular to shielding of enclosed spaces to ensure that such waves can neither enter nor leave.

Shielding of enclosed spaces from electromagnetic waves of radio frequency, in the range 104 to 3 x 1012 Hz, is normally required for security purposes. For example, computer equipment generates electromagnetic waves of radio frequency which carry the information used by the computer; if the computer is not in a shielded room, the waves can be picked up outside the room, and the information extracted. It is also important to ensure that waves of radio frequency generated outside an enclosed space cannot interfere with equipment inside. Shielding for waves of radio frequency normally comprises metal members sheets or meshes of a suitable size, all of which block the waves physically, and which are electrically earthed in order to ensure that the waves are not re-transmitted by the shielding.When shielding an enclosed space, it is important that there are no physical gaps in the shielding through which the waves can leak. Enclosed spaces are therefore normally shielded by lining with lead sheet, which effectively forms a continuous surface, except for an appropriately sealed door. Such lead shielding is effective, but expensive to install, and heavy, and does not provide a pleasant working environment, as there is no natural light, and the temperature can be difficult to control.

According to the present invention shielding of an enclosed space from electromagnetic waves of radio frequency is achieved by providing separate shielding means for each of the individual components defining the space without affecting their normal function, the interfaces between adjacent shielding means also being shielded.

This enables an ordinary room with for example, windows, doors and air conditioning to be shielded, without blocking daylight from the windows or affecting operation of the air conditioning, so providing a normal working environment.

Preferably the components are shielded by using metal foil or mesh, so that the shielding is cheaper and lighter than lead lining. The size of mesh is chosen in accordance with the frequency of the waves to be blocked; the higher the frequency the smaller the mesh.

According to a second aspect the invention comprises a screening glazing unit comprising a frame having a peripheral channel for receiving a transparent sheet, a sheet of glass received in the frame, and attachment means adapted to secure a sheet or film of screening material to an attachment area of the frame; the frame and transparent sheet being substantially impervious to radiation of the frequency and bandwidth chosen to be screened.

Preferably the frame comprises a plurality of separate elements held together so as to define interfaces between the elements.

According to a third aspect the invention comprises a screening door adapted to be fitted to a doorway, the door having longitudinally extending hinge means and first and second sealing means provided spaced from the hinge axis in a direction transverse to the hinge axis.

Preferably the first and second sealing means comprise loops extending around the peripheral regions of the door.

The first and second sealing means may be spaced from the hinge axis by different amounts. One loop of sealing means may be provided within another. The sealing means may be provided at different positions in the thickness of the door.

Examples of methods of shielding individual components of an enclosed space, such as a computer room, from electromagnetic waves of radio frequency are described with reference to the accompanying drawings of which: Figure 1 shows a room in accordance with the first aspect of the invention; Figure 2 shows a window installation in accordance with the second aspect of the invention for use in a screened room; Figures 3 to 6 show details of the window installation of Figure 2; Figure 7 shows a modification of the arrangement of Figure 5; and Figures 8 to 11 show details of a door in accordance with the third aspect of the invention for use in a screened room.

The shielding means for the components comprise metal members, foils or meshes providing a physical block to the passage of the waves, with the interfaces of adjacent shielding means connected in such a way that there are no physical gaps through which the waves can leak. For this reason, metal members such as aluminium must be bare, not anodised or coated, to ensure that firm continuous contact can be made with them. The shielding must also be electrically earthed to ensure that the waves are not re-transmitted by the shielding.

For a typical existing computer room, with a floor 3, walls 4, ceiling 5, windows 6, doors, fittings and ventilation systems 8, appropriate methods of shielding are as follows.

The floor 3 is shielded by a raised floor 9 of steel plate, of the type generally used for computers, with a layer of wire shielding mesh 10 bonded to the top surface of the plate. Carpets 11 or other floor finishes may be laid on the mesh.

The shielding for the walls is provided by a wall lining system comprising a steel framework 12 of horizontal top and bottom members interconnected by spaced vertical members, and clad with 13 mm laminated plaster boards 13 containing wire shielding mesh 14, held in firm continuous contact with the steel framework. The system is of the kind where the boards are provided with clips which hook over horizontal cross-members of the framework, so that the boards are held in position by their own weight. This creates the necessary firm contact between the framework and the mesh at the periphery of the boards. The bottom member of the framework is arranged so that it is in firm and continuous contact with the floor mesh 10. Any partitions within the room may be similarly constructed.

The ceiling 5 is shielded by a suspended ceiling 15, which may replace an existing one. The suspended ceiling comprises a standard suspended grid 16 of aluminium T-section bars, on which tiles are laid. The tiles are of plasterboard, covered with metal foil, and metal clips placed over the grid bars provide the contact between the foil and the bars.

Further shielding for the ceiling is provided by a wire mesh 18 located above the grid. The mesh and the peripheral members of the grid are each arranged to be in continuous contact with the top member of the wall framework.

Existing windows 6 are shielded by secondary glazing units 19' comprising a bare aluminium frame 19, in contact with or sealed to the wall framework, and glazed by clear laminated or toughened glass 20 coated on both sides with a multi-layer metallic coating which blocks the waves. The coating is in continuous contact with the frame. As an alternative, the glazing may comprise a wire mesh sandwiched between two sheets of glass; the wire mesh is then in contact with the frame. Suitable glazing units are described in more detail later.

Existing doors are replaced by shielded doors mounted in frames 21 connected to the wall framework.

Shielded doors 7 may have a solid core containing a wire shielding mesh, or comprise an aluminium frame glazed in the same way as the window glazing units.

The peripheral edges of either type of door may be provided with a gasket which may have the form of a wire coil covered with neoprene, to provide a shielding seal between the door and the frame when the door is closed. An alternative form of shielding for the doors 7 is described later.

It is of course necessary to provide services, such as power and light, to the room, and cables for these services are installed in shielded trunking. Any apertures in the wall lining or ceiling are sealed, for example by a gasket similar to that provided for the doors.

The ventilation or air conditioning system for the room requires a grille or grilles 8 through which air passes. Such a grille may be replaced by a shielded grille of wire mesh. The overall dimensions of the grille are chosen to allow the air flow required, while the mesh dimension is chosen to ensure that the required frequency of waves is blocked.

One of the shielding means, usually the floor shielding, is electrically earthed.

It is clear that the methods described above lead to complete shielding of a room from electromagnetic waves of radio frequency, while retaining the appearance of the room. In particular, the room will still have daylight and air conditioning or ventilation systems, so it provides a pleasant working environment. Shielding a room in this way is also relatively cheap, and light in weight.

If physical security is also required for a room, for example security sensors which detect any unauthorised attempt to enter the room, or armour material, these may also be incorporated in the shielded components.

Thus, optical fibre sensors, in the form of a mesh, may be provided to give continuous coverage of the surface area of the room. The mesh is preferably provided as sheets on the individual components of the shielded floor, wall lining and ceiling, and the sheets are then interconnected by cables. Optical paths are provided across the doors and windows. The optical fibre sensors are connected to a light transmitter and receiver which detect breaks in the mesh to set off an alarm. Optical fibre sensors are reliable, difficult to circumvent, as they cannot be bridged, and safe, as they carry only light.

Should armour material be required as part or a security system, this can readily be provided for the walls by replacing the plaster boards of the wall lining system by armour materials, such as GRP (glass reinforced plastic) armour or solid melamine. Doors can also be armoured appropriately, and the windows glazed with bullet resistant glass.

Details of another screened room are illustrated in Figures 2 to 11, and similar refeence numerals have been given to similar components.

Figure 2 shows a general view of a secondary glazing unit 19' adapted to be secured at an existing window 6 (shown in Figures 5 and 6).

Figure 3 shows detail of the connection of the glazing unit 19' to the rest of the room in which it is fitted, the detail being concerned with the connection of the plasterboards 13 to their support frame 12 and forming a continuous screen at the junction of the walls and floor of the room.

The floor 3 of the room is covered with a layer of 3mm stainless steel sheets 22 which screen the floor and take the place of the raised floor 9 and mesh 10 of the arrangement of Figure 1. A carpet 23 is laid over the sheets 22.

The walls 4 of the room are screened by a thin copper mesh 24 which is secured to the wall by -spacers 25. A false wall is constructed in front of the copper mesh 24 by means of a skeletal framework of aluminium section 26 similar to that shown in Figure 1, having horizontal and vertical members upon which conventional plasterboard panels 27 are hung. The panels 27 are hung from the cross-members using clips which hook on the cross-members, the panels being held to the framework by their own weight. Each panel 27 extends for substantially the full height of the room.

The mesh 24 extends under the framework 26 and under the peripheral edge region of the plates 23 to provide a continuous screen from the walls to the floor.

A skirting 28 is secured to the foot of the panels 27 and locates in a channel-section member 21 provided adjacent the carpet 23.

Figure 4 illustrates detail at the ceiling of the room and shows the existing ceiling 5 and wall 4, the skeletal framework 26, the copper mesh 24 extending over the top of the framework 26 to the other side of it, and a false ceiling comprising tiles 30 suspended on an aluminium support frame 31. The support frame 31 is fixed to the skeletal framework 26. Channel section 32 is secured to the plasterboards 27 and E-section beading 33 locates over the section 32 and extends to the support frame 31. The channel section 32, beading 33 and support frame 31 are all of aluminium.

The tiles 30 have a metal coating so as to be impervious to radiation of the desired frequency, and there is no straight-line path leading from the false ceiling upwards out of the room which does not hit the mesh 24, tiles 30, or support frame 31, all of which will not allow the radiation to pass.

A further mesh may be provided above the tiles 30 operatively connected to the mesh 24, if so desired.

The tiles 30 would then not need to be impervious to the radiation to be screened.

Figure 5 illustrates detail of the secondary glazing unit at the ceiling of the room. The secondary glazing unit 19' is mounted so as to screen an existing conventional window 6. The window 6 is provided in a window recess 6' extends upwards to the existing ceiling 5, and above the height of the false ceiling.

The secondary glazing unit 19' comprises a sheet of DATASTOP (Trademark) glass 3a mounted in an aluminium window frame 34. The frame 34 is formed by separate aluminium extrusions 35,36,37 and 38.

The DATASTOP glass is sealed to the frame 34 by three SOFTSHIELD (Trademark) seals 39'.

DATASTOP (TM) glass is available from Pilkingtons, the glass manufacturers, and is substantially impervious to radiation in the frequency range of interest. SOFTSHIELD seals are commercially available seals.

The window frame 34 comprises L-section aluminium extrusions 35 defining a rectangular mounting member 35' screwed to spacer members 42' which are in turn affixed to the window ledge (not shown), sides 40 of the window recess 6', and the upper surface 41 of the window recess 6'. Extrusions 36 are formed into a rectangular main frame member 36' having a generally h-shaped section. The extrusions 36 have, in section, abutment wall 42 which has a flat surface abutting a face of the spacer members 42' and a projecting limb of the L-shaped mounting member 35', a cross-wall extending away from the abutment wall 42 at an intermediate point in its length, and a spaced wall 44 extending from the end of the cross-wall 43 spaced from the abutment wall 42 and away from the centre of the window. The spaced wall 44 has a flange 45 extending into the channel defined between the three walls 42,43 and 44, and a spacing lug 46 provided at its outer peripheral end. The corner between the cross-wall 43 and spaced wall 44 has a projecting flange 47 extending towards the centre of the window. The cross-wall 43 has an outward step 48 at its central region and a locating lug 49 at the step 48. The abutment wall 42 is screwed to the projecting limb of the mounting member 35 at a position inwards of the cross-wall 43.

A ceiling skirting wall 50 is secured to the ceiling 5 in the region of the window 6 by means of a mounting batten 51 and carries the support frame 31 for the ceiling tiles 30. A spacer 52 is secured to the skirting wall 50 and abuts the spaced wall 44 so as to space the skirting wall 50 from the frame 34. The skirting wall comprises a plywood panel having a layer of aluminium foil 53 on its side nearest the window.

Extrusions 37 comprise channel-sections defining a rectangular glazing bead 37', the outer peripheral region of which is located relative to the main frame 36' by the co-operation of the flange 47 and lug 49 of the cross-wall 43. The bead 37' is screwed to the cross-wall 43.

The extrusions 38 have an L-shaped cross-section and define a rectangular lip frame 38'. The lip frame 38' is mounted on the spaced wall 44 with one limb of the L-section resting on the flange 45 and the other limb forming a lip to which copper mesh 18 (similar to the copper mesh 24 of the walls) provided over the false ceiling is operatively connected. The copper mesh 24 extends between the batten 52 and the ceiling 5 and is held to the lip of the frame 38' by a plastics clip 54. The clip 54 is of figure five cross-section having a flat upper plate and a sprung, curved lower portion. The clip 54 extends around the full length of the periphery of the frame 38'. The end of the copper mesh 24 is folded around the lip of the frame 38' and the clip 54 holds it firmly to the frame 38', the curved portion of the clip bearing against the spacer 52.

The parts of the extrusions 35-38 which are in contact with each other are plain aluminium, not anodised or coated, to ensure that good electromagnetic contact is made between the extrusions. This helps to ensure that the frame 34 does not leak electromagnetic radiation.

The glazing bead 37 is filled with conventional glazing sealant to seal the inside edge of the Datastop window.

The many bends and corners in the frame 34, and the many interfaces between separate extrusions 35-38 which make it up, help to reduce re-radiation of an electromagnetic signal by the frame 34.

It is believed that sharp changes in direction in the extrusions have the effect of allowing only certain frequencies to transmit around the bends. By having different bends at different spacings it maybe that mis-aligned transmission frequencies can be arranged so that no frequency of interest is transmitted by the frame 34 as a whole. It is also believed that the interfaces between separate extrusions assists in the attentuation of any signal.

A typical room containing computers has radiation 4 13 of a wide range of frequencies (10 Hz - 10 Hz) coming into it and interfering with its contents, for example computers, and, typically, a narrower range of frequencies eminating from its contents, for example computers tend to operate at 30 MHz. Thus the screening stops radiation entering and leaving the room.

Figure 6 shows detail of screening around the sides of the secondary glazing unit 19.

The window is set in a relatively deep false alcove 60 which is defined by the false wall (plasterboard 27), and a further sheet of plasterboard, sheet 61. Corner strengthening box section members 62 extend vertically adjacent the edges of the window.

The plasterboard sheets 27 and 61 are secured to the Figure 7 shows the use of an alternative sealing arrangement in place of the SOFTSHIELD seal of Figure 5. A beryllium-copper spring sealing strip 63 is provided along each edge of the Datastop glass pane. Each strip 63 is of channel-section having a spine which engages the edge of the glass 39 and two arms which extend to either side of the glass. Each arm terminates in a returned-curled resilient engagement portion 64 which bears against the sides of the glass 39. A locating and sealing mastic 65, or a TWINSHIELD (Trademark) seal is applied in a bead between the spine of the strips 63 and the cross-wall 43 of the frame. One arm of the strip 63 has a locating projection which is received in a notch in the abuting wall 36.

The door 69 to the room is illustrated in Figures 8 to 11 and comprises a rectangular frame 70 of box-section aluminium tube having spaced opposed side sheets 71 and 72 of steel overlaid with 4mm veneered plywood 73,74. The inside steel sheet 71 has on its outer surface (inside the hollow door) a fine copper mesh extending over the centre area of the sheet 71.

The door 69 is hinged by hinge 75 which is fixed to batten 76 which is in turn fixed to a hollow box-section aluminium extrusion which forms part of a rectangular door frame 77. The door frame 77 is provided adjacent an existing door opening of the room. False walls 78 are provided of plasterboard spaced from the existing walls 4 by a distance of about 100mm. Further plasterboard panels 79 are provided to give the doorway a neat appearance from the outside of the room.

At each side of the door the copper mesh 24 of the walls is held firmly against an aluminium T-section member 80 by a continuous spring clip 81, the T-section members and the clip extending for the full height and width of the doorway. The T-section members 80 are in operative engagement with the doorframe 77.

Figure 9 is a vertical section through the door and shows the screening above the door (between the doorframe 77 and the wall 4 leading to the ceiling) and at the floor 3 and also illustrates schematically a magnetic lock of the door which is more fully described later.

The door 69 is provided at each of its peripheral edges with an inner sealing lip 82 and an outer sealing lip 83 (best shown in Figures 10 and 11). The sealing lips are provided as L-section strips secured to the door. The peripheral lips 82 and 83 are received in complementary inner and outer (with respect to the screened room) seal strips 84 and 85 which are held in channel section members 86 connected to the doorframe 77. The inner lips 82 are at a slightly outward position compared with the position of the outer lips 83 when the door is viewed face-on, as can be seen from the Figures, the inner lips 82 surrounding the outer lips 83 (inner and outer refer to the positions relative to the sealed room).

When the door is opened the lips 82 and 83 move away from the sealing strips 83 and 85.

An example of a suitable sealing strip is the "schlegel C2EMI seal" (Trademark).

Details of the hinge arrangement are best seen in Figure 10. The hinge 75 extends for the full length of the door and is made of metal impervious to the screened radiation. It is screwed to a plate 87 which is in turn secured to the steel plate 71 on the inside face of the door. One of the lips 82 is also provided adjacent the hinge 75. The hinge is offset from the position of the lip 82, and seal strip 84.

There is significant protrusion of the lip 82, and indeed the lip 83, adjacent the hinge into their respective sealing strips 84 and 85. This ensures a good seal at the hinge. The channel member 86 in which the outer seal strip 85 is held is supported for additional strength by a box-section member 88 extending around the doorway. The hinge arrangement also avoids over-compressing the seals, which would occur if the seals were provided too close to the hinge, and so avoids damaging the seals.

The door is held closed by two magnetic locks 90 (shown in Figures 9 and 11). The door has ferromagnetic keeps which are attracted to electromagnets provided at the doorframe 77. Two magnetic locks are provided at the edge of the door spaced from the hinge, one spaced one quarter of the way from the top of the door and the other one quarter of the way from the bottom of the door. The locks 90 are provided in aluminium boxes 91.

The locks 90 are controlled by a push-button controlled electric circuit and hold the door shut with a force of about one tonne (say 17001bs). The electric circuit controlling the door includes a fail-safe device which automatically releases the door in case of emergency, such as fire. A fire detector may also be provided in the room and may have an electrical input into a control module for the door.

The screened room is thus in general appearance not very different from the original room, if a little smaller. It has windows, and can be treated in most ways as a normal room. For example, it is possible to hang pictures on hooks screwed to the false plasterboard walls without destroying the shielding of the room. Similarly, shelves can be attached to the walls. The fact that the screening mesh is behind a false wall spaced some way in front of it is useful in this respect.

Claims (27)

1. A shielded enclosed space having separate shielding means for each of the individual components defining the space, and shielded interfaces between adjacent shielded means, the individual components of the space still being capable of performing their useful functions.

2. A shielded enclosed space according to claim 1 having a shielded window and/or a shielded door.

3. A shielded enclosed space according to claim 1 or claim 2 in which screened walls, a ceiling, and a screened floor are provided over existing walls, ceiling and floor, the screened walls, ceiling and floor screening the space that they enclose.

4. A shielded space according to any preceding claim in which a screened wall is provided, the screened wall having a screening element spaced from a surface element, the surface element being presented to the space and defining in part the available room within the shielded space.

5. A shielded space according to claim 4 in which the screening element is sufficiently far away from the surface element that the surface element can be punctured without puncturing the screening element.

6. A shielded space according to claim 5 in which the surface element can take screws and nails without puncturing the screening element.

7. A screening or shielding wall having a screening sheet, film, or mesh spaced from a structural surface member, the screening sheet being spaced from the structural surface member by a distance sufficient to enable the surface member to bear drawing pins, or nails, without puncturing the screening sheet.

8. A screening glazing unit comprising a frame having a peripheral channel for receiving a transparent sheet, a transparent sheet received in the frame, and attachment means adapted to secure a sheet or film of screening material to an attachment area of the frame; the frame and transparent sheet being substantially impervious to radiation of the frequency and bandwidth chosen to be screened.

9. A unit according to claim 8 in which a plurality of separate elements are held together so as to define interfaces between the elements.

10. A screening door adapted to be fitted to a doorway, the door having longitudinally extending hinge means and first and second sealing means provided spaced from the hinge axis in a direction transverse to the hinge axis, the door and sealing means being substantially impervious to radiation to be screened.

11. A door according to claim 10 in which the sealing means comprise loops extending around the peripheral regions of the door.

12. A door according to claim 11 in which one loop is provided within the other.

13. A door according to claim 10 or claim 11 in which the sealing means are spaced from the hinge axis by different amounts.

14. A door according to any one of claims 10 to 13 in which the sealing means are provided at different positions in the thickness of the door.

15. A method of shielding an enclosed space comprising providing separate shielding means for each of the individual components defining the space, and providing shielding for the interfaces between the shielding means.

16. A method of shielding an enclosed space according to claim 15 in which the space is a room having a window and/or a door which are shielded as separate components to the remainder of the room.

17. A method of shielding an enclosed space according to claim 15 or claim 16 in which the space is a room and a screened floor, screened ceiling, and screened walls are provided.

18. A method according to claim 17 in which the screened floor, ceiling, and walls are provided over existing walls, floor, and ceiling.

19. A shielded space substantially as herein described and illustrated with reference to Figure 1 of the accompanying drawings.

20. A shielded space substantially as herein described and illustrated with reference to Figures 2 to 11 of the accompanying drawings.

21. A method of shielding a space substantially as herein described and illustrated with reference to Figure 1 of the accompanying drawings.

22. A method of shielding a space substantially as herein described and illustrated with reference to Figures 2 to 11 of the accompanying drawings.

23. A shielded wall substantially as herein described and illustrated with reference to Figure 1 of the accompanying drawings.

24. A shielded wall substantially as herein described and illustrated with reference to Figures 2 to 11 of the accompanying drawings.

25. A window unit substantially as herein described and illustrated with reference to Figures 5 and 6 of the accompanying drawings.

26. A window unit substantially as herein described and illustrated with reference to Figures 5 and 6 of the accompanying drawings, as modified by Figure 7.

27. A door substantially as herein described and illustrated with reference to Figures 8 to 11 of the accompanying drawings.